<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="a">小猫</div>
    <div class="a">小猫</div>
    <div class="a">小猫</div>
    <div class="b">小猫</div>
    <div class="c">小猫</div>
    <div class="d">
        <div>
            12345697
        </div>
    </div>
    <div class="f">
        <div>
            12345697
        </div>
        <div>
            12345697
        </div>
    </div>
    <style>
        #a {
            color: black;
        }

        .a {
            color: #000;
            background-color: rgb(220, 220, 220);
            font-size: calc(100vw - 100px)
        }

        * {
            color: aquamarine;
        }
    </style>
</body>

</html>